The sensorless drive of an induction machine has been studied for last two decades. And some of the results are applied to industrial fields (Reference 1,2). But the performance of the drive is still much inferior to that of the sensored drive. Especially, at low or zero stator frequency the torque control ability of the drive is still far from the satisfaction. At higher stator frequency, practically higher than 10% of rated frequency, simple direct vector control method based on the integration of the stator terminal voltages gives satisfactory torque control performance (Reference 3). Most of the sensorless drive algorithms are based on the assumption of d-q equivalent circuit of the induction machine (Reference 4-7), and hence they are dependent on the machine parameters and measurement errors. At low stator frequency region, signal to noise ratio of the stator voltage measurement is very poor and stator resistance voltage drop is dominant. At zero stator frequency, even theoretically no rotor dynamics can be measured at the stator terminals (Reference 8). With these reasons the sensorless algorithm based on d-q circuit fail at low and zero stator frequency region no matter how algorithm is superior. Another group of sensorless algorithms is using non ideal phenomenon of the machine characteristics such as eccentricity of rotor, rotor slot harmonics, and rotor unbalance (Reference 9,10). These algorithms need. frequency spectrum analysis, and they are time consuming and need some machine construction data such as number of rotor and stator slot, which can not be easily obtained from off the shelf. Even with newly developed FFT algorithm, still the performance of the speed control bandwidth of the drive looks like unsatisfactory (Reference 11). Third category of the algorithm is injecting some signals to the motor and checking the response of the motor to the injected signals (Reference 12.about.15). Most of these algorithms depend on the variation of rotor leakage inductance according to the intensity of the main flux. This algorithm gives reasonably satisfactory performance for the open rotor slot motor. But in the case of closed rotor slot, unfortunately most of small and medium power squirrel cage induction machine is the case, the algorithm does not work well especially at loaded operating condition because of similar saturation effect on the leakage inductance with load current flowing in rotor circuit. The torque controllability at low and zero frequency region could be a great asset to off-the-shelf general purpose inverter feeding conventional squirrel cage induction motor. So far, most algorithms do not work well with mass produced closed rotor clot motor in zero or low stator frequency region under heavily loaded condition.